design of stirling engine - research india publications · 2018-11-03 · design of stirling engine...

Design of Stirling Engine R B Venkata Murali1, G Tarun Naidu2, Challa Suresh 3, P Anil Kumar4, A Muniswamy5

Abstract: The objective of this paper is to build up a Stirling engine which is fit for working

on various heat sources. We are developing a prototype of γ-type Stirling engine which can

be examined for developing and designing a full-scale engine. We need to analyze the

performance, in all aspects with respect to temperatures, rpm and efficiency by giving heat

input to the system. After modifying and analysing the progressive improvements into a final

design by building, developing and testing the prototype. The prototype of same

configuration must be selected for a final design, such that our model can be developed by

scaling factor.

Keywords: Stirling engine, Design, Working model, Thermal efficiency.

1. INTRODUCTION:

In the time of 1816, the Stirling engine was initially patented by Robert Stirling. The

Stirling engine has pulled in more consideration throughout the years as this is mainly due to

its high productivity and capacity to utilize any assortment of sustainable fuel sources, which

has made it an option for power generation. The Stirling engine can be externally heated by

any warmth source with finite temperature difference which is preferred standpoint when

contrasted and different engines usually utilizes fuels and different gasses. It has high

efficiency because of its simple construction with less number of moving elements when

compare with internal combustion engines and less prone to dangerous failures.

1.1.Principle

The conversion of heat energy into mechanical energy by undergoing through the four

different process in a Stirling cycle. The basic processes involved are

P-V diagram

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 12, Number 1 (2017) © Research India Publications. http://www.ripublication.com

706

mailto:[email protected]





1. Isothermal expansion: The bottom end of the cylinder is maintained at high

temperatures so that the gas inside the bottom cylinder will undergoes isothermal

expansion process by taking heat energy from the source.

2. Constant volume heat rejection: The gas will be passing through the

regenerator, and here it gets cooled by exchanging heat energy to the regenerator

for further usage in the cycle.

3. Isothermal compression: The displacer will be at the bottom end such that the

pressure drop takes place which makes the power piston to go down and

compresses the gas inside the cylinder thus the isothermal compression takes

place in the cycle.

4. Constant volume addition: In this process the gas goes back through the

regenerator and it regains some heat which helps in heating the gas when entering

the expansion stage.

1.2.Types of Stirling Engine:

A. α-type: It consists of two power pistons. These pistons simultaneously compresses the

working gas in the cold end then moves it into the hot end, where it gets expanded and

afterward it moves backs. The cold end, regenerator and hot end are arranged in a

series manner. This kind of engine has more amount of power to volume ratio but

difficult to achieve due to inability of the durability of its seals.

α-type

B. β-type: In this type of configuration, the piston will do the compressing and expanding

work and the displacer will do the gas transfer process from hot end to cold end. The

displacer is arranged in a way that the power piston and the displacer are in same line

is known as β-type Stirling engine. In this type of configuration, the displacer piston

does not extract any work form the expansion of gas but simply used to transfer the

gas form hot end to cold end. This β- type keeps itself away from the issues of hot

moving seals.


707

β-type

C. γ-type: In this type of configuration, the piston will do the compressing and expanding

work and the displacer will do the gas transfer process from hot end to cold end. Here

the piston and the displacer are arranged offset from each other for a simple

mechanical advantage is known as the γ-type Stirling engine. Though there is an

offset between piston and displacer they were still in aligned to the similar flywheel.

The gas will flow freely in both the cylinders which makes it as a single unit. This

type has low compression-ratio, so it’s mechanically simpler and is frequently used in

Stirling engines of multi cylinder type.

γ-type

2. PROTOTYPE OPERATION:

Since the Stirling-engine is completely closed cycle, it contains a fixed mass of air called

the "working medium", most ordinarily air, helium, nitrogen, argon etc. During operation, the

engine’s working medium is fixed. Unlike Internal combustion engines it does not requires

valves mechanism. Stirling engine is almost similar to heat engines and cycles that runs on

four fundamental procedures: heat addition, expansion, cooling and compression. The gas

gets compressed in the power piston and it makes the displacer piston to change in its

position such that the working medium (air) is around the hot junction. The gas which is

heated with increased pressure will make the power-piston to reach its extreme power stroke

limit. Now the displacer-piston will move the air to the cylinder’s cold end. The gas which is

cooled, undergoes compression by the flywheel momentum.

2.1.Design Conditions:

The characteristics required for this type of design are as given below

The ratio of the swept volumes of the displacer to power piston must be very high.


708

The diameters of the displacer and displacer cylinder must be large.

The length of the displacer must be small.

The heat transfer must be effective on the surface of both plate ends of the displacer.

3. Material selection and dimensions

3.1. Heat exchanging surfaces:

The surfaces of heat exchanging is fixed by the available area at the heat rejection

system & it helps us to fix the displacer diameter and its height. In order to have high heat

transfer rate from the source to the system & from the system to atmosphere materials with

high thermal conductivity must be used. Some of the materials with above required features

for heat exchanging surfaces are as follows:

Eg: Copper, Aluminium, Mild steel, G.I (galvanized iron)

Aluminium material is used as a heat exchanging surface:

Thickness: 2mm

3.2. Displacer Cylinder:

It must be having good resistance property to heat transfer which means a material of

lower thermal-conductivity. So that the heat flow cannot be done from hot end to the cold end

of the cylinder body. In this displacer-cylinder the displacer performs its stroke. The working

medium gets transferred from displacer cylinder to the power piston cylinder through

regenerative pipes some of the materials possessing the above property are: Wood, Concrete,

Plastic, and Glass.

So we had selected an aluminium can as displacer cylinder.

Displacer Cylinder

Diameter: 5.92cm

Height: 7.4cm.

Volume: 203.76 cc

3.3.Displacer:

Displacer must be resistant to heat transfer and light in weight. So we have to select a

material having lo thermal conductivity and lower density. The types of displacer materials

available are Wood, Thermocol, Iron wool, Reinforced plastic. It displaces the working

medium (air) in between cold and hot ends.

So we had selected Steel wool material as displacer.


709

Displacer

Diameter of displacer: 5.92cm

Thickness of displacer: 4.0cm

Volume: 110.145 cm

4. Properties of working mediums:

S.No Working

Medium

Gas Constant(J

/kg.k)

Cp (J

/kg.k)

Cv (J

/kg.k)

Viscosity(N-

s/m2)

1 Air 287 1007 720 0.00003

2 Argon 208 523 315 0.00004

3 Carbon

dioxide

189 845 656 0.00002

4 Helium 2077 5200 3123 0.00003

5 Hydrogen 4120 14310 10190 0.000015

6 Nitrogen 296 1038 742 0.00003

We used air as a working medium as it is easily available.

5. Design of Cylinder & Power-piston Power-piston is the critical part of the Sterling engine, which produces the power

stoke by the expansion of the air in it. The friction between the cylinder and the power piston

is very less and the power stroke must be as same as the stroke of the displacer. Friction co-

efficient must be as lo low as possible in between the piston and cylinder, which also requires

proper lubrication.


710

Power-piston cylinder

The materials which requires the above requirement as follows:

S.No Piston Material Cylinder Material

1 Steel Wool Aluminum

2 Steel Steel

3 Epoxy Resin Glass or Steel

4 Brass Brass

Power piston stroke = 3.3 cm

6. Parts of the Stirling engine

6.1.Crankshaft:

Crankshaft is the mechanical device which converts linear motion into rotary motion

which also supports the flywheel. It’s made up of stainless steel with diameter of 0.2 cm and

length of 16.4 cm which has the phase angle difference of 900

Crankshaft

6.2.Flywheel:

A heavy mechanical device which is used in the increase of machine’s momentum

and also to provide greater stability. Here it is made of plastic, with the dimensions of 0.2 cm

in thickness and 12.2 cm in diameter.

Flywheel

6.3.Connectors:

Here connecters are used as the connection between the crankshaft & connecting rod.

Here it is made up of brass, with 2.5 cms in length & 0.5 cms in width.


711

Connectors

6.4.Connecting Rod:

A mechanical device which is used in connecting between any two moving parts,

especially in between the crank shaft and the piston.

Connecting Rod

FINAL ASSEMBLY OF STERLING ENGINE


712

Final assembly

7. Expenses of Materials

Name of the Part Quantity Material Used

Disposal Coke tins 3 Aluminum

Flywheel 1 Plastic

Supports for crankshafts 2 Aluminum

Crank shaft 1 Stainless Steel

Power piston 1 Rubber Diaphragm

Power piston cylinder 1 Plastic

Displacer cylinder 1 Aluminum

Connecters 10 Brass

Regenerative Pipes 2 Rubber

Displacer 1 Steel wool

Heat source(spirit lamp) 1 Steel

8. Graphs:


713

9. Conclusion:

In this project, we have fabricated a Stirling engine and assembled as per the

required procedure. The assembly made is running with good rpm. As per the ASME

standard Stirling engine produces 17% of the efficiency.

After Testing of the prototype is determined with low range of heat input to the

system could give higher rate of efficiency as the temperature difference is very much high

and good at no load conditions.

10. REFERENCES: 1. G. Thombare and S. K. Verma, "Technological development in the Stirling cycle engines," Renewable

and Sustainable Energy Reviews, vol. 12, pp. 1-38, 2008

2. F. Formosa and G. Despesse, “Analytical model for Stirling cycle machine design,” Energy Convers.

Manag., vol. 51, no. 10, pp. 1855–1863, Oct. 2010.

3. Minassians, A. D., Stirling Engines for Low-Temperature Solar-Thermal-Electric Power Generation,

Ph.D. thesis, University of California - Berkeley, 2007

4. A. C. Ferreira, S. F. C. F. Teixeira, J. C. Teixeira, M. L. Nunes, and L. B. Martins, “Modeling a Stirling

Engine for Cogeneration Applications,” in Proceedings of the ASME 2012 International Mechanical

Engineering Congress & Exposition IMECE2012, 2012, pp. 1–9.


714

5. R. S. Khurmi& J. K. Gupta, “Textbook of Machine Design”, S. Chand Publications, 14th Revised

Edition (2005), pp. 1138-1160

6. J. R. Senft, An Introduction to Low Temparature Differential Sitrling Engines, Moryia Press, River

Falls, WI, 1996.

7. Abdullah, S., Yousif, B.F. and Sopian, K. (2005) ‘Design consideration of low temperature differential

double-acting Stirling engine for solar application’, Renewable Energy, Vol. 30, No. 1, pp.1923–1941

8. Asnaghi, A., Ladjevardi, S.M., Saleh Izadkhast, P. and Kashani, A.H. (2012) ‘Thermodynamics

performance analysis of solar Stirling engines’, ISRN Renewable Energy, Vol. 2012, p.14.

9. Kang, S-W., Kuo, M-Y., Chen, J-Y. and Lu, W-A. (2010) ‘Fabrication and test of gamma-type Stirling

engine’, PEA-AIT International Conference on Energy and Sustainable Development: Issues and

Strategies. Karabulut

10. B. Kongtragool and S. Wongwises, "A review of solar-powered Stirling engines and low temperature

differential Stirling engines," Renewable and Sustainable Energy Reviews, vol. 7, pp. 131-154, 2003.


715

design of stirling engine - research india publications · 2018-11-03 · design of stirling engine...

Documents